Native New Zealand forget-me-nots (Myosotis, Boraginaceae) comprise a Pleistocene species radiation with very low genetic divergence

Abstract

Reconstruction of molecular phylogenies is an important step towards understanding the evolutionary history of island plant radiations. The New Zealand forget-me-nots (Myosotis, Boraginaceae) comprise a lineage of over 40 closely related but morphologically and ecologically diverse species whose evolutionary history and taxonomy are unclear. Myosotis is a high priority for systematic research in New Zealand because a high proportion of these species are threatened, and many have restricted geographic ranges and occupy very specific habitats. Here, we investigated the relationships and age of Southern Hemisphere forget-me-nots by performing phylogenetic, molecular dating, and other analyses of DNA sequence datasets from representatives of nearly all described species. To this end, we used both chloroplast (atpI–atpH + rps16–trnQ) and nuclear ribosomal (ITS + ETS) DNA sequences, as well as amplified fragment length polymorphisms (AFLPs). Our analyses showed that genus Myosotis likely arose in the Northern Hemisphere during the Miocene with the ancestor of the Southern Hemisphere lineage arising in the Pleistocene and radiating shortly thereafter. The Southern Hemisphere Myosotis species have very low levels of genetic divergence and their relationships are largely unresolved, likely due to a combination of recent radiation, hybridization, and incomplete lineage sorting. Our results are compared to those of similar studies on other New Zealand species radiations, and implications for ongoing and future Myosotis taxonomic and evolutionary research are discussed.